Atmospheric seals



April '15, 1969 N ET AL 3,438,617

ATMOSPHERIC SEALS Filed April 10. 1968 INVENTORS Gerome Gordon 8:

/ George J. Barth, Jr.

United States Patent US. Cl. 26340 7 Claims ABSTRACT OF THE DISCLOSURE An improved atmospheric seal to close-off a work area of a heat treating furnace such as a coil annealing furnace or the like. It has ceramic fibrous material of density between to 20 pounds per cubic feet placed in a sealing trough. The seal is effectuated by the weight of a removable work cover on the fibrous material, the work cover having rounded and/or flat end portions in contact with the fibrous material.

This application is a continuation-in-part of patent application Scr. No. 601,400, filed Dec. 13, 1966, now abandoned.

This invention relates to atmospheric seals which are used to close-off the interior work area of a heat treating furnace and the like from the outside atmosphere. It is particularly useful in eifectuating an efiicient and simple seal composed of coherent solid material without the use of a secondary seal or a cooling system or a structurally complex furnace base and/ or work cover.

The use of a seal to atmospherically close-off the interior work area of a heat treating furnace and the like from the exterior heating portions of the furnace and outside atmosphere is broadly old and well known. It allows a protective atmosphere to be established and eificiently maintained in the work area enclosed by a removable work cover during the heating operation, thereby preventing an unwanted chemical reaction such as oxidation from occurring with the metal surfaces of the work pieces being heat treated. Such seals can repeatedly withstand temperatures above 1700 F. for extended periods of time without resulting deleterious effect to its physical properties and without chemically modifying the protective atmosphere in the work area. Such atmospheric seal has heretofore been commonly accomplished by forming a trough in the furnace base into which sand was placed. When the work cover was positioned to begin the heat treating operation, knife-like end portions of it would sink into the sand under its own weight and effect an atmospheric seal. Because of the particulate nature of the sand, however, the particles would become entrained in the protective atmosphere within the work area and in turn would be deposited on the surface of the work pieces being treated. This residue would, in turn, damage processing machinery if it was not first removed from the surface of the work pieces before further processing after the heat treating operation. For example, if steel coils were annealed in an annealing furnace having a sand seal, temper rolling could not be accomplished without damice age to the steel rolls of the mill if the residue sand was not first removed. Further, because of permeability of the sand, additional sand had to be piled around the outer circumference of the work cover by hand labor to reduce wasteful leakage of protective gas.

Previously, various seals have been proposed which eliminate the sand and in turn eliminate the above-stated problems by effecting a seal composed of coherent solid material. But these proposed seals were impractical to fabricate, operate and replace because of their complexity. Such proposed seals incorporated one or more of the following variants: a secondary seal to reduce permeability, an extensive cooling system to keep the seal at a low temperature so that its parts would not be destroyed, or a structurally elaborate work cover and/or base to position the seal away from the area of intense heat.

The present invention overcomes these disadvantages and makes an etfic-ient and simple atmospheric seal composed entirely of coherent solid material commercially feasible. Further in our invention permeability can be reduced by approximately 5 to 6 times the permeability which was available with the use of the sand seal.

We provide an atmospheric seal to close-off the interior work area of a heat treating furnace and the like from the heating means and the outside atmosphere. The components of a seal are a removable work cover; a furnace base having a sealing trough therein, preferably of a U-shape, to receive end portions of the work cover; and a ceramic fibrous material of a density within a certain range and fiber structure placed in the sealing trough in the furnace base. When the work cover is placed over work pieces to begin the heat treating operation, the weight of the work cover compresses the ceramic fibrous material increasing its bulk density and decreasing its permeability, and in turn effecting the atmospheric seal.

The ceramic fibrous material is a silica base material which is able to repeatedly withstand temperatures above 1200 F. and preferably 1700 F. for extended periods of time under a pressure of approximately 7 to 10 p.s.i., remain both chemically and physically inert to "both the outside atmosphere and the inside protective atmosphere, and still return to substantially the same density when the work cover is removed. The ceramic fibers are randomly oriented to provide the permeability of the material and are of the short staple type to provide the durable qualities of the seal under continued use.

Further, the ceramic fibrous material must have a density within a certain range so as to avoid deep penetrat'ion of the end portions of the work cover into the fibrous material under the weight of the work cover. The difiiculties encountered when the work cover does deeply penetrate into the fibrous materials are (i) that the fibers of the material become broken or meshed and lose their resiliency, and in turn the permeability of the seal is impeded, (ii) that the fibrous material separates from the outside walls of the trough and in turn the heat insulating qualities of the seal are impeded, and (iii) that the fibrous material becomes entangled with end portions of the work cover and is mined away when the work cover is removed.

We have found that the ceramic fibrous material, when placed in the trough, need have a density between 5 t0 20 pounds per cubic foot, depending upon the specifics of the material used, the form of the material used, and the way in which it is placed into the trough. When the material chosen is of a bulk form having substantially the same properties throughout, it should have a density, after being packed in the trough, in the range of 15 to 20 pounds per cubic foot, with 18 pounds per cubic foot being the most desired density. When the material chosen is of a matted form, we have found that lower density material can be used because of the inherent properties of the matted material, and further that the material need not be backed in the trough. In addition when the matted form is chosen, it is desirable that the material be a laminate having ceramic fibrous material of higher den sity toward the bottom of the trough and material of lower density in contact with the work cover. The gross density of the laminate will depend upon the ratio of lower density material to higher density material. We prefer that the higher density material be the larger portion of the laminate and most desirably be between 60% :and 85% by volume of the laminate. We prefer that the density of the laminate should be of a lower density than with the bulk material, but not be less than 5 pounds per cubic foot.

We prefer that the ceramic fibrous material be of the matted form and be a laminate. By using this form, we can prefabricate the sealing material and install it with a minimum of time and labor. Additionally, repair of the seal can be effected easily and with a minimum of labor. Also, by having the material in matted form, the seal is not subject to impairment by blow outs which occur during the annealing operation.

We also prefer that the laminate have a crown adjacent its upper surface. When the work cover is placed in position the fibrous material thus compresses so that the top surface is substantially planed. In this way, the Working life of the seal is increased by adding resiliency to the seal.

The work cover has rounded and/ or fiat end portions which engage the ceramic fibrous material in the sealing trough when the work cover is positioned for the heat treating operation. The rounded end portions of the Work cover prevent cutting and permanent meshing of the ceramic fibrous material and avoid deep penetration of the work cover when the work cover is in position. When flat end portions only are used they must be large enough to distribute the weight of the work cover over a large area of the fibrous material for the same reason. We prefer that the end portions be fabricated by welding a steel ring with a solid cross-section to the work cover, or by mechanically rolling integrated end portions of the work cover.

Other details, objects and advantages of our invention will become apparent as the following description of the presently preferred embodiment thereof proceeds.

In the accompanying drawing, we illustrate a presently preferred embodiment of our invention in which:

FIGURE 1 is a partial cross-sectional view of a single stack coil annealing furnace showing our atmospheric seal in operation with the bulk ceramic fibrous material;

FIGURE 2 is a partial cross-sectional view of our atmospheric seal with a laminate ceramic fibrous material having a crown thereon;

FIGURE 3 is a partial cross-sectional view of our atmospheric seal in operation with a laminate ceramic fibrous material having a crown thereon and FIGURE 4 is a partial cross-sectional view of our atmospheric section in operation with a laminate ceramic fibrous material and a Work cover with end portions having large fiat areas in contact with the ceramic fibrous material.

Referring specifically to the drawings, an atmospheric seal is comprised of a base 2 of a single stack coil annealing furnace having a circulating fan 3 with a power means 4, cooling coils 5, and a U-shaped sealing trough 6 therein. In the sealing trough 6 is packed a ceramic fibrous material 7 in bulk form, having a density of 18 pounds per cubic foot. The fibrous material is a short staple fiber, such as the fiber tradenamed Fiberfrax, produced by the Carborundum Company. Base 2 supports the hearth 8 which in turn supports the work pieces 9 in Work area 10. The work area 10 is enclosed by a removable work cover 11 which has substantially straight cylindrical sides 12 and end portions 13. The end portions 13 engage the ceramic fibrous material 7. The end portions 13 are composed of a solid steel ring which is welded to the work cover 11 so that the ceramic fibrous material 7 compresses the latter and effects the atmospheric seal. Around the work cover 11 is an insulating shell 14 containing the heating elements of the annealing furnace. Because of the relatively straight sides 12 of the work cover 11, the atmospheric seal is positioned in the intense heat of the furnace without cooling or shielding means.

In a preferred embodiment, the ceramic fibrous material 7' is a laminate, having a crown 15 thereon. Two rings 16 of a matted B & W Kaowool (made by Babcock & Wilcox) is placed in the trough 6 in layers, a third ring 17 of matted Fiberfrax (made by Carborundum), having a narrower width, is concentrically placed in the trough 6 to provide a third layer, and a ring 18 of matted short staple Fiberfrax is placed in the trough 6 thereover to form the crown 15. In operation, the crown 15 will compress so that the surface 19 of the crown 15 becomes planed under the weight of the work cover 11'.

In another preferred embodiment, the ceramic fibrous material 7" is a laminate and the work cover 11" has end portions 13" with large flat surfaces 20. The large flat surfaces 20 of end portions 13" contact the ceramic fibrous material 7" to distribute the weight of the work cover over a large area and thereby prevent cutting and permanent meshing of the ceramic fibrous material 7" and deep penetration of the work cover 11" when it is positioned.

While we have shown and described a certain present preferred embodiment and use of our invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and used.

We claim:

1. An atmospheric seal for closing-off an interior work area of a heat treating furnace and the like from an outside atmosphere which comprises a removable work cover, a furnace base having a sealing trough herein, and a ceramic fibrous material having a density between 5 and 20 pounds per cubic foot provided in the sealing trough, whereby end portions of the work cover engage the ceramic fibrous material and effect the atmospheric seal by weight of the work cover thereon.

2. An atmospheric seal for closing-off an interior work area of a heat treating furnace and the like from an outside atmosphere is claimed in claim 1 wherein the ceramic fibrous material is in a bulk form and has a density between 15 and 20 pounds per cubic foot.

3. An atmospheric seal for closing-off an interior Work area of a heat treating furnace and the like from an outside atmosphere as claimed in claim 1 wherein the ceramic fibrous material is in a matted form and is a laminate.

4. An atmospheric seal for closing-off an interior work area of a heat treating furnace and the like from an outside atmosphere as claimed in claim 3 wherein the laminate is composed of at least two different ceramic fibrous materials, one of higher density than the other, and wherein the ceramic fibrous material of higher density is overlayed with the ceramic fibrous material of lower density.

5. An atmospheric seal for closing-off an interior work area of a heat treating furnace and the like from an outside atmosphere as claimed in claim 4 wherein the ceramic fibrous material of higher density is between 60 and 85 percent by volume of the laminate.

6. An atmospheric seal for closing-off an interior work area of a heat treating furnace and the like from an outside atmosphere as claimed in claim 1 wherein end portions of the work cover have a large flat surface whereby the weight of the work cover is distributed over a large area of ceramic fibrous material.

7. An atmospheric seal for closing-01f an interior work area of a heat treating furnace and the like from an outside atmosphere as claimed in claim 3 wherein the laminate has a crown adjacent upper surface portions.

6 References Cited UNITED STATES PATENTS JOHN J. CAMBY, Primary Examiner.

US. Cl. X.R. 

